The movie begins with seaside views of Mallorca, Spain. In a hotel bathroom is Tammi (Nichola Burley) face-up in the bathtub. She gets up from the tub and starts to shave her armpits when she accidentally cuts herself. Her friends Lisa (Sian Breckin) and Kim (Jaime Winstone) come in and Lisa tells her that she’s gorgeous; Tammi says no, she’s a mess.

DONKEY PUNCH TRAILER

They leave the bathroom and sit on the beds and Kim tells them that they’re going to love the place that they’re going to. Tammi gets a text message on her phone but Lisa takes it before Tammi could get to it. Lisa sees that it’s Ryan and Tammi immediately wants her phone back. Kim takes it from Lisa, and tells Tammi that he’s toxic, sending Ryan a text reply, and gives the phone back to Tammi. Tammi sees that Kim wrote “F*CK OFF 4EVR!” to Ryan and laughs but Tammi tells Kim that she doesn’t believe her. Lisa tells Tammi that she promised that she would have no contact with Ryan (who we should assume is Tammi's ex), and she pours them all vodka, toasting to “Tammi for being brave” and for their upcoming fun weekend together.

As some credits roll, we see the three girls getting into a taxi and going to various bars, drinking, having fun, and flirting with a bunch of guys. At one place, they meet a group of guys. One of them asks what they’re drinking, and Kim answers champagne. He says he’s paying and says his name is Marcus (Jay Taylor) and the collective group of Marcus and his friends and Kim and her friends end up stealing a bottle of champagne and taking it out with them.

While sitting at a beach, Tammi and Lisa are talking and they can’t believe that they were just at rainy Leeds and now they’re in sunny Mallorca. The three girls are hanging out on the beach with the guys when Kim asks what they all want to do next. Her friends don’t want to go to another bar so one of the guys tell them that they’re welcome to hangout in their yacht. The girls learn that the guys are crewmen, not owners of the yacht. Lisa agrees for all of them and they make their way to the boat.

On the dock, Lisa and Kim are excited, laughing with the boys and having fun. However, Tammi is obviously not sure about going with the boys and she overhears one guy telling the other guys that everything’s going “according to plan”. Before they all get on, Tammi tells her friends that she might just go back to the hotel since she thought that it was supposed to be just the three of them for the weekend. Kim is fine with catching up with Tammi later, but Lisa tries to talk Tammi out of it and to just come on the boat for a drink.

The guys call out to a guy on the boat named Sean, the boat’s engineer, and Lisa convinces Tammi to get on the boat. Kim learns that Sean and Josh are brothers. The girls see how large the boat’s downstairs area is and Josh gives them a tour of the boat and shows them the different bedrooms as well as the engine room.

While Josh is giving the girls a tour, the guys talk about who they’re going to have. Bluey (Tom Burke) calls dibs on Kim, while Marcus gets Lisa, meaning that either Josh or his brother Sean get Tammi. The group party upstairs and Kim tries to make the music louder. However, Sean tells the group that they can’t have the music too loud on the dock or they’ll get in trouble. Kim says they’re going to leave, and the guys then suggest that they have their party on the high seas. Sean reluctantly agrees. Tammi is outside and Sean comes and flirts with her, teaching her how to unwind the rope tying the boat to the dock.

Bluey comes up on deck and gives them all ecstasy pills. They all take a whole pill except for Tammi and Sean who each take a half. They anchor out and they swim in the ocean except for Bluey. They start talking about sex positions like Dirty Sanchez and Turkey when Bluey asks the group if they’ve heard of a Donkey Punch. Marcus claims to have done it before and Bluey explains what it is (during anal sex, punching the back of the girl’s head at the right time to get a better orgasm). Meanwhile, Tammi is in the water with Sean and she talks about not wanting to go back to Leeds because there are people there she doesn’t want to see anymore.

Later on, Bluey has some smoking paraphernalia and claims that his drug is hardcore, in which Lisa answers that she is hardcore so she takes a hit and so does Kim. Bluey also gives Josh a hit. Kim, Bluey, Marcus, and Lisa go downstairs and start making out in the master bedroom when Josh comes down to watch. Bluey takes out a video camera and starts taping Lisa and Kim making out. Kim tries to get the guys to makeout but instead the guys have a competition on who has the best butt.

Up on deck, Sean and Tammi are talking about their most recent past relationships. Sean’s being that the girl messed around with him and Tammi’s ex cheated on her with a close friend of hers. Tammi gets up to put some music on when she realizes that everyone else had gone downstairs. When she tells Sean that even Josh is gone, Sean is worried for a bit and is about to go downstairs but then Tammi starts making out with him.

Meanwhile downstairs, Kim starts making out with Marcus even though she’s really supposed to be with Bluey so Lisa takes Bluey and they all have sex in the master bedroom with Josh still watching them and videotaping the whole scenario. Then Bluey gets Lisa to let Josh “have a go” at her. Lisa and Josh are having anal sex with Bluey videotaping them and coaching Josh on when Bluey refers back to the Donkey Punch and tells Josh to do it, so Josh punches Lisa at the back of her head and she falls down.

There is obviously something wrong and Kim and Marcus stop what they’re doing. Josh leaves the room in a hurry and Marcus goes out on the deck to tell Sean to come inside. Downstairs, Kim is huddled on the couch and we see Marcus checking for Lisa’s pulse. Sean comes in and checks her pulse and says he thinks she’s dead. When the girls asked what happened, Bluey doesn’t respond and Sean says that she must have overdosed. The girls leave the room and Sean says that he’ll alert the Coast Guard. However, Josh says that they shouldn’t as there would be no point and they would be gone by the time they got there. Sean suspects that something else went on.

Downstairs, Bluey and Josh talk about what just happened. Josh says that he didn’t do anything but Bluey says he saw Josh. Marcus wants to know what really happened and Bluey tells Marcus that Josh donkey punched Lisa, but Josh starts to say that Bluey told him to, but Bluey denies it. Bluey tells Josh that the Donkey Punch is just a story and no one actually does it. Marcus cannot believe that it happened so Bluey shows him the videotape.

Kim and Tammi are in another bedroom and Kim tells Tammi that she feels that Bluey and Josh are acting weird. Tammi asks, and Kim says that they were shouting and filming when Lisa died.

Marcus finishes watching the tape and is angry at Josh for getting them all involved. The three boys go on deck to Sean and Marcus has Josh tell his brother what happened. Sean watches the tape and Josh asks Sean for his help. Marcus shuts off the yacht power and Marcus says that since there’s a girl downstairs with a broken neck and that their DNA is all over her, they’re all going down for the crime. Josh suggests that they could say that she fell overboard.

Downstairs, Kim and Tammi are freaking out because their cell phones don’t have service.

Upstairs, the guys continue talking about what they should do, as Sean points out that Kim and Tammi aren’t going to agree to lie about Lisa falling overboard. Bluey suggests that they dump the two girls as well which makes Sean freak out and say that it’s Bluey’s fault that this happened because he supplied the drugs and told the stories. Bluey says that Josh did it and Josh tells him to shut up and not to push his luck and surprisingly, Bluey listens to him. Bluey apparently throws the tape out into the sea. The guys continue talking about the situation and agree that they can’t go to the police and get in trouble as well. Still Sean says that someone needs to tell the girls.

Downstairs the guys sit the girls down and say that they should all do the right thing. When Tammi asks what that means, Marcus tells her that as far as the Coast Guard was concerned, Lisa fell overboard. Tammi says that they’re mental. Marcus asks the girls how long they’ve known Lisa for, and if they want to be the ones to tell Lisa’s parents how she really died. Marcus says that he just wants what’s best for everyone. Kim says that she knows that Josh killed Lisa, and that it’s all on tape. Josh denies there being a tape and Marcus says that a decision has been made. Marcus and Josh go to the master bedroom where Lisa’s body is covered in a bedsheet. Marcus lifts the sheet up and sees a dark bruise on the back of Lisa’s neck. Sean comes in and helps Marcus carry the body out when Josh points out that they have to be in international waters and Sean tells him to shut up. Marcus says that they need to do it now and while the girls are still scared. Up on deck Marcus gives Josh instructions to stop the boat and anchor. While they’re tying up Lisa’s body to be thrown overboard, Sean says that it’s not right but Marcus says that he’s worked too hard to have his brother mess it all up and that this way everyone gets their lives back. Sean says “Not everyone…”

Downstairs, a scuffle goes on between Kim and the guys. Bluey is holding Kim back and Josh is holding Tammi. Kim claims that she’s going to tell the police, while Josh retorts that that would mean telling the police about the drugs that she did and how she was having sex with a stranger. Kim gets away from Bluey’s hold and takes a knife from the kitchen. She manages to get up on deck and points the knife at Marcus to stop them from throwing Lisa overboard. Marcus gets the knife away from Kim and Bluey comes to hold her as they dump Lisa’s body into the sea.

Sean and Marcus throw Lisa’s body overboard, but it floats up, so Marcus gets in the water to put a weight on the body so that it sinks down. While Marcus is in the water, Kim and Tammi run to the boat controls and make the boat start going again while Marcus is still in the water, so he almost gets caught in the propellers.

Marcus gets out safely though, and the girls downstairs try to look for something that would put them in contact with help. Tammi is in the guys’ room and Sean finds her there and offers her his jacket. He tells her that they are the only two on the boat that are sane, but Tammi is angry at him for helping the guys get rid of Lisa’s body. Sean want to sincerely help Tammi, and tells her that she just needs to keep Kim in control.

Bluey and Josh are in the control room and talk about how they could’ve lost Marcus in the sea and that they need to look out for each other. Josh suggests that with Marcus being the acting skipper of the boat however, it would be all Marcus’ fault. Bluey realizes that Josh is trying to blame everything on Marcus, so Bluey shows Josh that he didn’t throw the videotape evidence away into the sea like they thought he did. Obviously, Josh only cares about keeping himself looking innocent.

Marcus finishes his shower and finds that Bluey is waiting for him right outside. Josh is walking around looking for Marcus to tell him that Bluey still has the tape and Kim tells him that he’s in the shower but makes a point to talk about dropping the soap and anal sex which angers Josh and he throws Kim into a room. Josh then sees Tammi and asks the same thing. Marcus followed by Bluey walks towards them and tells Tammi that they have 45 minutes until they hit international waters and that everyone was going to stay there so that he can keep an eye on everyone. Bluey tells the girls to make them all a meal.

Over dinner, Josh tells Marcus, with 20 minutes left, that Bluey kept the tape. Sean freaks out because this means that Josh is going to get all the blame. Marcus asks Bluey what he’s going to do with the tape and Bluey says he’s going to put it on the Internet and that Josh was going to be a Youtube superstar. Marcus asks the girls if they’re going to do the right thing. Tammi apparently gives in however, and tells them that she was going to tell the police that Lisa died from an alcohol overdose. Bluey tells them that he doesn’t like the fussing and fighting and tries to touch Kim and Tammi tells him to leave her alone. Bluey says that Tammi is just jealous that Kim gets all the attention and says that was probably why her boyfriend was sleeping around, going as far as betting that Kim slept with Tammi’s ex (which turns out to be true, explaining why Kim told Tammi that Ryan was toxic in the beginning of the movie). Bluey continues to talk and Tammi angrily stabs him on the shoulder with the bread knife. Marcus tries to choke Tammi and Sean pulls him off. Kim pulls Tammi away into a room and locks it. Sean knocks and tells her to open the door but they leave through the roof and get on the life raft away from the boat.

However, they left without the motor and Kim lets out a flair so the guys could find them again instead of drifting off in the sea. The boat comes and Sean throws them a rope but Marcus comes with a shotgun telling the girls to get out of the boat. Kim takes Marcus by surprise and fires a flare into Marcus and Marcus, now on fire, flails around, and falls into the ocean and dies.

Sean brings Tammi and Kim back inside, past where Bluey is still sitting in the same place from when he got stabbed by Tammi, and into the guest bedroom. Josh locks them in there and Sean is in the control room and turns off all the power. Sean tells Josh that they need to find the keys. Josh finds the keys in the master bedroom but tells Sean that Marcus must have had them on him. Sean tells Josh to call for help since Bluey needs to get properly treated for his stab wound. Again, Josh doesn’t do it and instead hides the communicator. Josh carries Bluey into the bathroom and tries to get him to say where the tape is.

Tammi runs through the glass door to get out of the room they were locked in and gets cut on her knee on some glass. Josh is using Bluey’s cocaine to get Bluey to tell him where he hid the tape and it works, and Bluey says that it’s under the bed. Tammi is passing by the bathroom and overhears Bluey so she gets to the tape first and hides. Josh looks for the tape under the bed and can’t find it. Tammi is hiding in the closet and Josh runs back to the bathroom and thinks that Bluey was lying to him, so Josh pushes the knife still in Bluey’s shoulder farther in while Bluey screams in pain. Tammi knocks on the door and tells Josh to leave Bluey alone because he doesn’t have it. Josh hears this and takes the knife out of Bluey. Josh comes out of the bathroom and sees Tammi and tells her that Bluey died because he lost too much blood but Tammi knows what happened and calls him a liar. Kim comes and has the shotgun and aims it at Josh.

With the gun still aimed at him, Kim gets Josh to start the boat again and says that he can’t communicate with anyone because Marcus reset all the channels (really Josh hid the communicator). Josh says that if Sean is in the engine room, he could die in there so Tammi leaves Josh and Kim alone to get Sean. Tammi finds Sean and gets him out of the engine room. Meanwhile Josh tells Kim that if Tammi gave the tape in as evidence then even she would get in trouble, so if they helped each other and stuck to the same story then they could both come out from it clean. Josh tricks her and gets the gun and runs down to shoot Tammi. Sean gets the gun away from Josh but Kim thought that Sean was shouting at Tammi instead of Josh, so she grabs the outboard motor (the one that belongs to the dingy), starts it up, and uses it like a chainsaw on Sean.

Tammi is angry at Kim for killing Sean, because Sean was trying to help them. Kim runs up to the deck and commits suicide by throwing herself overboard because she feels bad about killing Sean.

Tammi and Josh are the only ones left and decide that they can’t be found on the boat so they get on the life raft. When they're a good distance away from the boat, Josh takes a knife out of his pocket and threatens Tammi with it, telling her to throw the tape away. She throws it at him but at the same time she throws a rope connected to the boat around his neck, pulling him back and breaking his neck.

Tammi is now alone on the life raft and lets out a flare. The movie ends with her laying on the life raft the way that she was laying in the bathtub at the beginning of the movie.

*CUT TO THE CHASE*
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Three British girls and four Spanish guys get on a yacht together to party. During sex, one of the guys tries the “donkey punch,” and ends up killing one of the girls. The act was recorded on a tape, and the rest of the film revolves around who has the tape, who gets the blame, and who goes to jail. It’s more or less guy versus girl, and everyone dies except for Tammi, who escapes on a dingy but her fate is left unknown.